The investigators want to compare the effects of two drugs, levosimendan and milrinone, on cardiac muscle, both in terms of contractility and relaxation. Half of the participants will be randomized to each drug. The effects will be measured through echocardiographic deformation analyses.

Since deformation analyses could be dependent on different loading conditions of the heart, a second purpose of the study is to investigate the changes on deformation parameters after applied changes in preload and afterload, but also heart rate.

Aortic stenosis is associated with myocardial hypertrophy and diastolic dysfunction. In patients undergoing open aortic valve replacement surgery due to stenosis, the investigators want to compare the effect on myocardial relaxation between two commonly used drugs, levosimendan and milrinone, using catheter-based measurements in combination with echocardiographic evaluation.

Standard anaesthesia and surgical care for these patients is performed. After surgery is completed and the participant is transferred to the intensive care unit, the studies are performed during general anaesthesia and the participants still connected to a respirator with controlled ventilation.

Echocardiographic data will be collected simultaneously with hemodynamic parameters - first at two control measurements, then after each of two different doses of the drug. Preload, afterload and heart rate will be kept stable during this intervention. The echocardiographic data is later analyzed offline for strain and strain rate.

To further investigate the dependency of strain and strain rate on changes in preload, afterload, and heart rate, these variables are consecutively changed prior to drug administration. For this purpose, all patients first have their baseline data recorded, thereafter are paced at two different rates, then preload and afterload is altered by passive leg elevation and phenylephrine, respectively. Hemodynamic and echocardiographic data are collected simultaneously at baseline and after each intervention. Before administration of the drugs, baseline conditions are restored.

Inclusion Criteria:

• Subject has aortic valve stenosis
• Subject is scheduled for open heart aortic valve replacement with or without simultaneous coronary artery bypass grafting

Exclusion Criteria:

• Less than normal systolic function, defined as ejection fraction less than 0,5
• Non-sinus rhythm
• Any major surgical complication
• Problems understanding the informed consent